Lift pump control systems may be used for a variety of fuel system control purposes. These may include, for example, fuel injection vapor management, injection pressure control, temperature control, and lubrication. In one example, a lift pump supplies fuel to a higher pressure fuel pump (DI pump) that provides a high injection pressure for direct injectors in an internal combustion engine. The DI pump may provide the high injection pressure by supplying high pressure fuel to a fuel rail to which the direct injectors are coupled. A fuel pressure sensor may be disposed in the fuel rail to enable measurement of the fuel rail pressure, on which various aspects of engine operation may be based, such as fuel injection. Furthermore, a lift pump may be operated to apply just enough fuel pressure to the DI pump in order to maintain volumetric efficiency of the DI pump while preserving fuel economy.
However, the inventors herein have identified potential issues with such systems. The lift pump pressures applied to maintain DI pump efficiency may be low, especially during cold fuel conditions, thereby reducing performance of jet pumps inside the fuel tank, which can cause low fuel tank and jet pump fuel reservoir levels. Low fuel tank and low jet pump fuel reservoir levels can lead to low fuel line pressures, fuel vaporization within the fuel system, and a precipitous drop in DI fuel rail pressure, causing the engine to stall.
In one example, the above issues may be addressed by a method comprising: increasing a lift pump voltage to a high threshold voltage responsive to a DI pump volumetric efficiency being below a threshold volumetric efficiency, and increasing a lift pump voltage to a first threshold voltage less than the high threshold voltage responsive to a main jet pump fuel reservoir level being less than a first threshold reservoir level. In this way, the technical result of maintaining jet pump fuel flow and performance while preserving DI pump efficiency may be achieved. Accordingly, a risk of fuel vaporization within the liquid fuel delivery system and large DI fuel rail pressure drops can be reduced, and engine operation robustness may be increased while maintaining fuel economy.
In one example, if the DI pump volumetric efficiency decreases below a threshold volumetric efficiency, the lift pump voltage will be increased to a high threshold voltage in order to mitigate the DI pump volumetric efficiency drop and to restore the DI pump volumetric efficiency to the threshold volumetric efficiency. Furthermore, in response to a fuel reservoir fuel level decreasing below a first threshold reservoir fuel level, the lift pump voltage may be increased to a second threshold voltage less than the high threshold voltage. In this manner, both engine operation with low DI fuel pump efficiency, and fuel vaporization arising from low fuel reservoir levels and low jet pump flow can be mitigated while preserving fuel economy.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.